Device for measuring the current flowing in an inductive load

ABSTRACT

A device measures the current in an inductive load using two separate current-measuring paths to detect the current in the inductive load. The inductive load is connected between first and second nodes, and the first node connected to a first voltage. The device includes first and second transistors cascaded together between the first node and a third node that is connected to a second voltage. First and second sense amplifiers measure the current in the inductive load. The first and second sense amplifiers are connected to at least one terminal of the first and second transistors. Two blocks sample and hold signals from the first and second sense amplifiers, which represent, respectively, the currents in the two separate current-measuring paths. The two currents are subtracted in a comparison node for generating an error signal that is compared with a predefined window and if outside the window a failure signal is generated.

BACKGROUND Technical Field

The present description relates to the technical problem of themeasurement of current that flows in an inductive load.

One or more embodiments may find application in the automotive fieldwhere a high level of integrity of safety is required.

Description of the Related Art

The fundamental characteristics of devices for measuring current ininductive loads are the following:

-   -   regulation of current is carried out with the        pulse-width-modulation (PWM) method, where the driver        periodically connects at least one of the two terminals of the        inductive load to the positive supply and the negative supply,        at a pre-set frequency;    -   when just one of the two terminals of the load is driven in PWM        while the other remains constantly connected to one of the two        supplies, positive or negative, the current in the inductive        load flows in a unidirectional way; this is typically the case        of a solenoid for automotive applications that regulates the        pressure of a fluid (oil) with the purpose of actuating various        mechanisms, such as:        -   control of the braking system with ABS/ESP function; and        -   control of the automatic or servo-assisted change            (transmission control);    -   when both sides of the load are driven in PWM the current in the        inductive load can flow in both directions; this is typically        the case of the winding of an electric motor, because the latter        must be able to turn in both directions;    -   the current in the inductive load can assume, during operation,        values regulated with continuity from a minimum value, close to        zero, up to a maximum value specified during design of the        system; and    -   the device for measuring the current respects the most stringent        standards (ASIL-D) as regards functional safety (ISO-26262),        ensuring identification of a single failure point wherever this        may be located.

Normally, in the solutions currently in use, it is chosen to guaranteefunctional safety with two separate and independent current-measuringpaths.

By comparing the results of the two measurements performed on the twodifferent paths it is possible to evaluate whether:

-   -   the two measurements differ for a value lower than a pre-set        maximum error; if so, they are both judged correct, and the        device for measuring the current is free from faults; and        whether:    -   the two measurements differ for a value higher than a pre-set        maximum error; if so, one of the two measurements is not correct        (even though it is not known which one is not correct), and the        device for measuring the current presents a fault.

As is known, the measurements of current have a short propagation delayand a high frequency response in so far as they are set within a controlloop.

Some known solutions will now be described with reference to FIGS. 1, 1a, 1 b, 1 c, 1 d, and 2.

Illustrated in FIG. 1 is the operating principle of some knownsolutions. In particular, the device for measuring the current comprisesa load driver device Load Driver and uses two=separate current-measuringpaths in order to detect the current I_(L) that flows in the inductiveload Inductive Load connected between two nodes D and Q. The node D isconnected to the positive voltage V_(POS).

The device comprises two N-channel MOSFETs, in particular a high-sidepower transistor HS and a low-side power transistor LS, cascadedtogether and connected between the node D and a node G. The node G is inturn connected to the negative voltage V_(NEG).

Consequently, the device has a high side and a low side.

The source terminal of the MOSFET LS is connected to the node G, whereasthe drain terminal of the MOSFET HS is connected to the node D. Theintermediate point between the two MOSFETs is connected to the centralnode Q.

Flowing in the high-side MOSFET HS is the current I_(L-HS), whereasflowing in the low-side MOSFET LS is the current I_(L-LS).

Connected to the line that is connected to the node Q are twocurrent-sense amplifiers CSA₁ and CSA₂, which sense the current I_(L)that flows in the line (i.e., the same that flows in the inductiveload).

In a comparison node, the two currents are added (the second withnegative sign): the output of the comparison node generates the failuresignal Fail.

In particular, the failure signal Fail notifies the case where thedifference of the outputs of the amplifiers falls outside a predefinedwindow.

In the timing chart of FIG. 1, there may be seen the plots of thecurrents I_(L), I_(L-HS,) and I_(L-LS), respectively, corresponding tothe plot of the voltage V_(Q) measured on the node Q.

Illustrated in FIG. 2 is an example of implementation of a knownsolution.

In particular, having two separate current-measuring paths requiresduplication of the measurement resistors R_(S1), R_(S2). Consequently,with this implementation there will be further voltage drops on theduplicated measurement resistors R_(S1), R_(S2).

With reference to FIGS. 1a , 1 b, 1 c, and 1 d, there will now beintroduced the main limits of the known solutions.

For instance, the known solution illustrated in FIGS. 1a and 1b does notdetect the errors due to the losses introduced by the shown leakageresistors RH_(LEAK), RL_(LEAK), the reason being that they do not causeany difference in the two current-measuring paths.

Instead, the known solution illustrated in FIG. 1c detects failure ofthe current-sense amplifiers (CSAs) because they cause different resultsin the two current-sensing paths.

The known solution makes it also possible to detect the losses due tothe leakage resistors RH_(LEAK) and RL_(LEAK) as shown in FIG. 1d ,because they cause different currents in the two current-sensing paths.However, they have a higher likelihood of occurrence of dispersionlosses on the outer side of the inductive load (as illustrated in FIG.1a ).

The known solution illustrated in FIGS. 1 and 2 presents a drawback interms of cost. In fact, doubling of the in-series resistances forcurrent measurement leads to an increase (which is a degradation) of thetotal impedance seen between the pins of the integrated device. Inparticular, the path from the node D to the node Q is made up of R_(S1),R_(S2), and R_(HS), whereas the path from the node Q to the node G ismade up of R_(S1), R_(S2), and R_(LS).

In order to keep the impedance of the two paths unaltered, it isnecessary to oversize both of the power transistors HS and LS so as toreduce their impedance R_(HS), and R_(LS) by an amount equal to theadded series resistance rendered redundant for the measurement ofcurrent.

The known solution is able to diagnose the presence of a fault only inthe current-measuring components (FIGS. 1c and 1d ). Instead, todiagnose faults in the power transistors HS and LS and in the loadInductive Load in the form of leakage resistances towards one of thesupplies (FIGS. 1a and 1b ), it is necessary to add purposely providedcircuits.

BRIEF SUMMARY

According to one or more embodiments, a device for measuring the currentthat flows in an inductive load comprises a device for driving theinductive load and uses two separate current-measuring paths in order todetect the current that flows in the inductive load. The inductive loadis connected between a first node and a second node, and the first nodeis connected to a first voltage. The device comprises a first transistorand a second transistor cascaded together and connected between thefirst node and a third node connected to a second voltage.

The device further comprises a first sense amplifier and a second senseamplifier for measuring the current that flows in the inductive load.The first sense amplifier is connected to at least one terminal of thefirst transistor, and the second sense amplifier is connected to atleast one terminal of the second transistor. The measurement devicecomprises two blocks for sampling and holding the signals at output fromthe first and second sense amplifiers, which represent, respectively,the currents that flow in the aforesaid two separate current-measuringpaths. The two currents are subtracted in a comparison node forgenerating an error signal, which is compared in a window comparatorwith a predefined window, and if the error signal assumes values outsidethe predefined window the device generates a failure signal.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

One or more embodiments will now be described, purely by way of example,with reference to the annexed drawings, wherein:

FIGS. 1, 1 a, 1 b, 1 c, 1 d, and 2, regarding solutions belonging to theprior art, have already been described; and

FIGS. 3-12 are examples of various embodiments of a device for measuringthe current that flows in an inductive load.

DETAILED DESCRIPTION

In the ensuing description, one or more specific details are illustratedin order to provide an in-depth understanding of the examples of theembodiments. The embodiments may be obtained without one or more of thespecific details, or with other methods, components, materials, etc. Inother cases, known operations, materials or structures are notillustrated or described in detail so that certain aspects of theembodiments will not be obscured.

Reference to “an embodiment” or “one embodiment” in the framework of thepresent description is intended to indicate that a particularconfiguration, structure, or characteristic described with reference tothe embodiment is comprised in at least one embodiment. Hence, phrasessuch as “in an embodiment” or “in one embodiment” that may be present inone or more points of the present description do not necessarily referprecisely to one and the same embodiment. Furthermore, particularconformations, structures, or characteristics may be combined in anyadequate way in one or more embodiments.

The references used herein are provided merely for convenience and hencedo not define the sphere of protection or the scope of the embodiments.

In particular, the solution proposed does not interfere, reducing theperformance in terms of speed, with the known solutions illustrated inFIGS. 1, 1 a, 1 b, 1 c, 1 d and 2.

Parts that are the same as one another in the various devices formeasuring current in inductive loads illustrated in the various figuresare designated by the same references.

Consequently, the similar blocks already described with reference to thefigures regarding the solutions of prior art will not be describedagain.

With reference to FIG. 3, an embodiment of the solution described hereinmeasures the current of the inductive load Inductive Load separately onthe path of the high-side MOSFET HS and on the path of the low-sideMOSFET LS.

Various embodiments of the solutions proposed exploit the principle ofthe inductive current that does not change significantly at the momentwhen there is switching from the transistor HS to the transistor LS, andvice versa.

The comparison between the two currents is not continuous in time as inthe known solution, but is made between the current of the low-sideMOSFET LS an instant before this turns off and the current of thehigh-side MOSFET HS an instant after this has turned on. In this case,in the embodiments described herein, the comparison is made between thetwo currents at the maximum peak where there is passage from conductionof the transistor LS to conduction of the transistor HS.

In particular, in the embodiment illustrated in FIG. 3, two differentcurrent-measuring paths detect the current I_(L) of the load that flowsin the transistor HS and in the transistor LS.

In particular, the device for measuring the current is driven at inputby a control signal corn. In greater detail, the gate terminal of thehigh-side MOSFET HS receives the control signal corn inverted by theinverter 10, while the gate terminal of the low-side MOSFET LS receivesthe control signal corn in a direct way via the stage 12.

The current I_(L) in the inductive load is reconstructed by adding, inan adder SUM, the contributions of the two high-side and low-sidesections, in particular by adding the outputs of the current-senseamplifiers (CSAs).

The maximum current peak is sampled and held (S&H) separately on thepath of the high-side transistor HS and on the path of the high-sidetransistor LS, respectively, via the two sample-and-hold blocks S&H₁ andS&H₂.

For instance, in various embodiments, the sample-and-hold blocks S&H canbe obtained with very simple sequential electronic circuits, such asflip-flops. In particular, the signal present on the input terminalD_(IN) at the next enable signal supplied at input on the clock terminalCK passes at output as signal D_(OUT).

Furthermore, the control signal corn inverted by the inverter stage 14,denoted as com, is used as activation signal (or clock signal) forenabling the sample-and-hold blocks S&H₁ and S&H₂.

In particular, the inverted signal com is brought at input as signal Sdirectly on the clock input of the block S&H₂, whereas it is firstdelayed by a delay block 16 and then sent at input as signal s_(del) onthe clock input of the block S&H₁.

A subtractor node SUB generates the error signal err as the differenceof the outputs of the two sample-and-hold blocks S&H₁ and S&H₂.

A window comparator 18 generates a failure signal Fail in the case wherethe error signal err falls outside a predefined window. Hence, theresulting failure signal Fail indicates the case where the maximum peaksof the currents in the transistors HS and LS differ by a predefinedvalue.

The waveforms appearing in FIG. 3 represent, respectively, the voltageV_(Q) on the node Q, the current I_(L) on the inductive load, thecurrents I_(L-HS) and I_(L-LS) in the two respective separatemeasurement paths (and the output signals of the sample-and-hold blocksS&H_(1output) and S&H_(2output)), the delayed clock signal s_(del), theclock signal S, and the control signal corn. In this case, the waveformsreproduced show that the outputs S&H_(1output) and S&H_(2output) of thesample-and-hold blocks S&H₁ and S&H₂ are at a level that corresponds tothe maximum peak, where there is the passage from conduction of thetransistor LS to conduction of the transistor HS.

In various embodiments, the comparison can also be made between thecurrent that flows in the transistor HS an instant before this turns offand the current that flows in the transistor LS an instant after thishas turned on (see, for example, FIG. 6).

With reference to FIG. 6, in this case the comparison is made betweenthe two currents at the minimum peak, where there is passage fromconduction of the transistor HS to conduction of the transistor LS.

In this embodiment (FIG. 6), unlike the embodiment of FIG. 3, thecontrol signal corn is used as activation signal (or clock signal) forenabling the sample-and-hold blocks S&H₁ and S&H₂. Furthermore, in thiscase the inverter stage 14 is not necessary.

In particular, the delay block 16 is replaced by a delay block 16′ seton the low-side path, for generating a signal s_(del), which is sent atinput as clock signal of the block S&H₂.

In this case, the waveforms reproduced show that the outputsS&H_(1output) and S&H_(2output) of the sample-and-hold blocks S&H₁ andS&H₂ are at a level that corresponds to the minimum peak, where there ispassage from conduction of the transistor HS to conduction of thetransistor LS.

In various embodiments, it may be envisaged that the checks are made onboth of the peaks, as illustrated in FIGS. 7 and 8.

Illustrated in FIGS. 7 and 8 is a possible variant of the embodiments,which represents a combination of the principles proposed in theembodiments of FIGS. 3 and 6. In particular, in this case both of themaximum and minimum current peaks are sampled and held (S&H) on the twotransistors HS and LS separately with the two blocks S&H₁ and S&H₂,respectively. The filtering block combines and averages the values ofthe minimum and maximum peaks of the two transistors HS, LS in such away as to:

-   -   separate the signal from the noise; and    -   accept or reject various types of failure.

In FIG. 7 a finite-state machine is present, which generates the signalss₁ and s₂ that are required for driving the filter. The filter receivesat input the two values S&H_(1output) and S&H_(2output) at output fromthe sample-and-hold blocks S&H₁ and S&H₂ and generates the value err atoutput.

In particular, FIG. 8a shows the detection of the failures.

Detection of the failures due to the leakage resistances RH_(LEAK) andRL_(LEAK) is guaranteed irrespective of whether they are inside oroutside the load driver device Load Driver. In particular, in FIG. 8a ,which exemplifies an embodiment, the two leakage resistances RH_(LEAK)and RL_(LEAK) are within the load driver device Load Driver.

Also indicated are the two leakage currents that flow in the tworesistors RH_(LEAK) and RL_(LEAK), which can be calculated as:

${IH}_{LEAK} = \frac{V_{POS} - V_{NEG}}{{RH}_{LEAK}}$${IL}_{LEAK} = \frac{V_{POS} - V_{NEG}}{{RL}_{LEAK}}$

FIG. 8b shows the waveforms in the case of a classic filter with thefollowing characteristic:

${err} = {\frac{1}{n}{\sum\limits_{i = 1}^{n}\; \left( {{{{{S\&}H_{2,i}} - S}\&}H_{1,i}} \right)}}$

In particular, the filtering block:

-   -   subtracts corresponding samples S&H_(j,i) with j=1,2; in this        way, it detects the failures of the leakage or dispersion        currents IH_(LEAK) and IL_(LEAK); it also detects, with the same        principle, errors in the gain chain of the two current-sense        amplifiers CSA₁ and CSA₂; and    -   averages the “n” samples; in this way it reduces the noise of        the individual samples.

The criterion of acceptance is that the difference of the measurementsshould be lower than a pre-set maximum error; instead, if the error ishigher than a maximum value, it is not accepted. Consequently, in allthe figures representing the solutions described herein, a windowcomparator always appears.

With reference to FIG. 4, the first of the two samplings is made on thetransistor LS before it turns off, as in FIG. 3. Instead, the secondsampling is made after calculation of the difference between the sampleof the transistor HS just turned on and the previously stored sample ofthe transistor LS.

In particular, a subtractor node SUB1 calculates the value err1 asdifference between the value of the current that flows in the transistorHS and the value of the current that was flowing at the previous instantin the transistor LS and was previously stored in the block S&H₂.

The second sampler S&H₁ in this case must store a difference that isnormally close to zero and in any case must exceed the pre-set maximumerror only slightly. Consequently, in this case, the second sampler S&H₁receives at input the value err1, samples it, stores it, and makes itavailable at output at the next clock signal. Consequently, the signalat output from the second sampler S&H₁ represents the error err.

The second sampler S&H₁ presents the advantage of greater simplicity inso far as it requires a lower accuracy, because the difference iscalculated before, and a smaller storage capacity, because thedifference signal has a lower value.

With reference to FIG. 5, the second sampler S&H₁ is shifted evenfurther downstream with respect to the solution of FIG. 4, in particularafter the window comparator. The final result (signal Fail) remainsunaltered after this modification. The advantage for the second samplerS&H₂ is even more marked since it becomes a flip-flop in so far as ithas to store just one logic information bit (low level “0” or high level“1”).

Consequently, the embodiment illustrated in FIG. 5 follows the sameprinciple as the solution illustrated in FIG. 4, where the secondsampler S&H₁ has been shifted after the window comparator.

The advantage of this embodiment is represented by the fact that thesecond sampler S&H₁ has a minimal complexity since it processes asingle-bit digital signal.

With reference to FIG. 6, the comparison of currents may also be madebetween that of the transistor HS an instant before this turns off andthat of the transistor LS an instant after this has turned on. In thiscase, the comparison is made between the two currents at the minimumpeak where there is passage from conduction of the transistor HS toconduction of the transistor LS.

The passages described in FIGS. 4 and 5 also apply to the embodiment ofFIG. 6.

In particular, the same principle as that of the embodiment of FIG. 3applies, where the minimum peak current is sampled and held (S&H) on thetwo, high-side and low-side, portions separately by the two blocks S&H₁and S&H₂, respectively.

As already said, the operating principle of this embodiment also appliesto the solutions proposed in FIGS. 4 and 5.

FIG. 9 shows a further alternative embodiment.

In the solutions proposed according to FIGS. 3 to 8, the measurement ofcurrent can be made via two series resistances, which, however, areactivated just one at a time. Consequently, there is a minimal impact onthe series resistance of the total impedance seen between the pins ofthe integrated device. In particular, the path from the node D to thenode Q is made up of R_(S1) and R_(HS). Furthermore, the path from thenode Q to the node G is made up of R_(S2) and R_(LS).

The solution proposed consequently adds just one series resistance oneach of the two paths. Consequently, the power transistors do notrequire any oversizing with respect to the case of current measurementin the absence of redundancy for functional safety.

FIG. 10 shows a further alternative embodiment.

In particular, in this embodiment, the current is sampled on the drainand on the source of the two transistors HS and LS.

This embodiment adopts a known practice alternative to the measurementof current according to FIG. 9, i.e., that of using the power MOStransistor (HS and LS), which, when it is turned on, has an impedanceequivalent to that of a resistance (R_(HS) and R_(LS), respectively).With this solution, the measurement of current has a zero impact on theseries resistance of the total impedance seen between the pins of theintegrated device. Consequently, the path from the node D to the node Qis only constituted by R_(HS). Instead, the path from the node Q to thenode G is only constituted by R_(LS).

With respect to the embodiment proposed in FIG. 9, the current-detectionresistances R_(S1) and R_(S2) are obtained with the resistances R_(HS)and R_(LS), respectively, of the power MOS transistors. In this way, thetotal impedances on the paths HS and LS are due just to theON-resistance of the power MOS transistors themselves, and consequentlythe size of the circuit area is minimized.

In the embodiments proposed according to FIGS. 3 to 9, the measurementof current may be made via the power MOS transistor (HS and LS), as inthe case of the known solution, without any drawbacks.

In all the solutions proposed up to FIG. 10, an analog-to-digitalconverter is introduced on both of the outputs of the CSA, andconsequently all the subsequent functions are implemented in digitaltechnology.

FIG. 11 shows by way of example the digital evolution of the embodimentof FIG. 7.

In particular, in FIG. 11 the analog-to-digital converters (ADCs) havebeen introduced.

All the solutions proposed describe a load with one side connected tothe positive supply; however, the same solutions apply also in the caseof a load with one side connected to the negative supply, or else withboth sides of the load driven.

Some types of inductive load, such as the solenoids of automotivebraking systems, show a current that varies fast after switching of thedriver.

All the solutions proposed up to FIG. 11 would calculate an error err₀even in the case of normal operation in the absence of failures. Thiserror would be rather high with respect to what there would be in thecase of failure. It is consequently necessary to erase this error priorto sending the result to the input of the window comparator.

In general, this error err₀ depends upon the characteristics of theinductive load and the operating conditions to which it is subjected(supply voltage, average operating currents, temperature, etc.).

The solution proposed in FIG. 12 is a table that estimates the value oferr₀ on the basis of the operating conditions mentioned above and asubtractor that subtracts it from the measurement obtained with any ofthe embodiments proposed up to FIG. 11.

FIG. 12 reproduces a case of inductive load with fast time constant.

In this case, the waveform of the load current is a steep exponentialrather than triangular, as in the previous figures. All the embodimentsproposed for this case show a high value of err₀ also in the case ofnormal operation.

In this case, the solution proposed is an additional block thatsubtracts the above value of err₀ upstream of the window comparator thatmakes the decision as to whether there is a failure or not. This valueis stored within a table that takes into account all the independentvariables that affect the value itself, such as: the supply voltage ofthe driver load; the average current in the load; and the temperature ofthe load.

Without prejudice to the underlying principles, the details and theembodiments may vary, even appreciably, with respect to what has beendescribed purely by way of example, without thereby departing from thesphere of protection, as this is defined by the annexed claims.

The various embodiments described above can be combined to providefurther embodiments. These and other changes can be made to theembodiments in light of the above-detailed description. In general, inthe following claims, the terms used should not be construed to limitthe claims to the specific embodiments disclosed in the specificationand the claims, but should be construed to include all possibleembodiments along with the full scope of equivalents to which suchclaims are entitled. Accordingly, the claims are not limited by thedisclosure.

1. An electronic device, comprising: a first node configured to receivea first supply voltage a configured to be coupled to a first terminal ofan inductive load; a second node configured to be coupled to a secondterminal of the inductive load; a third node configured to receive asecond supply voltage; a switching circuit coupled to the first, secondand third nodes, the switching circuit configured to couple the firstnode to the second node in a first operating mode and to couple thesecond node to the third node in a second operating mode; a currentsensing circuit coupled to the switching circuit, the current sensingcircuit configured to sense a first current between the first node andthe second node in the first operating mode and to generate a firstsensed current signal based on the sensed first current, and configuredto sense a second current between the second node and the third node inthe second operation mode and to generate a second sensed current signalbased on the sensed second current; an output circuit coupled to thecurrent sensing circuit and configured to generate an error signal basedon a difference between the first sensed current signal and the secondsensed current signal, and configured to generate a failure signal basedon the error signal.
 2. The electronic device of claim 1, wherein theoutput circuit comprises a subtraction circuit configured to subtractthe first sensed current signal from the second sensed current signal togenerate the error signal.
 3. The electronic device of claim 2, whereinthe output circuit comprises window comparator configured to generatethe failure signal in response to the error signal, a first thresholdvalue, and a second threshold value.
 4. The electronic device of claim3, wherein the output circuit further comprises a first sample and holdcircuit and a second sample and hold circuit.
 5. The electronic deviceof claim 4, wherein the first sample and hold circuit is configured toreceive a first clock signal and the second sample and hold circuit isconfigured to receive a second clock signal, the first clock signalbeing delayed relative to the first clock signal.
 6. The electronicdevice of claim 5, wherein the first sample and hold circuit is coupledto receive first sensed current signal and the second sample and hold iscoupled to receive the second sensed current signal.
 7. The electronicdevice of claim 6, wherein each of the first and sensed current signalsis an analog signal, and wherein the output circuit further comprisesfirst and second analog-to-digital converters configured to convert thefirst and second sensed current signals into first and second digitalsensed current signals, respectively.
 8. The electronic device of claim1, wherein the switching circuit comprises: a first transistor includinga first signal node coupled to the first node and a second signal nodecoupled to the second node, and including a control node configured toreceive a first control signal; and a second transistor including afirst signal node coupled to the second node and a second signal nodecoupled to the third node, and including a control node configured toreceive a second control signal.
 9. The electronic device of claim 8,further comprising a first resistive element coupled between the secondsignal node of the first transistor and the second node and a secondresistive element couple between the second node the first signal nodeof the second transistor.
 10. The electronic device of claim 8, whereinthe current sensing circuit comprises: a first current sensing amplifiercoupled to the first and second signal nodes of the first transistor; asecond current sensing amplifier coupled to the first and second signalnodes of the second transistor.
 11. The electronic device of claim 8,wherein the first transistor and the second transistor are powerN-channel MOSFET transistors.
 12. The electronic device of claim 1,wherein the first supply voltage is a positive voltage and the secondsupply voltage is a negative voltage, or the first supply voltage is anegative voltage and the second supply voltage is a positive voltage.13. The electronic device of claim 1, wherein the output circuit isconfigured to generate the error signal at a maximum current peak ofeach of the first and second sensed current signals occurring at passagefrom conduction of the second transistor to conduction of the firsttransistor.
 14. The electronic device of claim 1, wherein the outputcircuit is configured to generate the error signal at a minimum currentpeak of each of the first and second sensed current signals occurring atpassage from conduction of the first transistor to conduction of thesecond transistor.
 15. An electronic device, comprising: a first nodeconfigured to receive a first supply voltage a configured to be coupledto a first terminal of an inductive load; a second node configured to becoupled to a second terminal of the inductive load; a third nodeconfigured to receive a second supply voltage; a switching circuitcoupled to the first, second and third nodes, the switching circuitconfigured to alternately couple the first node to the second node andthe second node to the third node; a current sensing circuit coupled tothe switching circuit, the current sensing circuit configured to sense afirst current between the first node and the second node and to sense asecond current between the second node and the third node; a circuitcoupled to the current sensing circuit and configured to generate anerror signal based on a difference between the sensed first and secondcurrents and configured to generate a failure signal based upon theerror signal.
 16. The electronic device of claim 15, wherein the circuitis configured to activate the failure signal responsive to the errorsignal exceeding a threshold value.
 17. The electronic device of claim15, wherein the threshold value is a window defined by a first thresholdvalue and a second threshold value.
 18. A method, comprising: applying asupply voltage to a first node; coupling the first node to a secondnode; sensing a first current flowing through an inductive load coupledto the first and second nodes and between the first node and the secondnode; applying a reference voltage to a third node; sensing a secondcurrent flowing through the inductive load and between the second nodeand the third node; generating a current error signal based on thedifference between the sensed first current and the sensed secondcurrent; and generating a failure signal based upon the error signalhaving a value outside a window defined by a first threshold value and asecond threshold value.
 19. The method of claim 18, wherein generatingthe failure signal comprises activating the failure signal in responseto the error signal having a value outside a window defined by a firstthreshold value and a second threshold value.
 20. The method of claim18, wherein sensing the first current flowing comprises sensing thefirst current a delay time after coupling the first node to the secondnode and wherein sensing the second current flowing comprises sensingthe second current before coupling the first node to the second node.